Many of the diseases known as inborn errors of metabolism result from the deficiency of a specific enzyme. In these cases one method of therapy is to administer the enzyme to affected individuals. However, since enzyme deficiency diseases occur only rarely, one problem in this approach has been to devise and test methods for preparing pharmacologically suitable enzymes. In the present proposal this problem had been overcome by using scurvy as a model enzyme deficiency disease. Scurvy is an illness caused by ascorbic acid deficiency. It is a result of the inherited lack of the enzyme L-gulonolactone oxidase in certain species of animals. Because the aberration is homozygous and readily available in a common laboratory animal, the guinea pig, numerous approaches can be tested without careful breeding or involved therapeutic maintenance of diseased animals. The research effort can then be limitrd to developing enzymes suitable for therapeutic use and studying pharmacologic aspects of enzymes as drugs. In preliminary studies we have developed a simple procedure that detoxifies administered L-gulonolactone oxidase. Using this procedure we have demonstrated that an inherited metabolic disease can be treated by administration of the missing enzyme. One objective of the proposed experiments is to extend and verify this finding. In addition, numerous procedures for chemical modification and immobilization of enzymes have appeared. Although many of these have been developed primarily for use in the production of enzyme products, they may also prove to be useful in enzyme replacement therapy. Another objective will be to test other chemically modified forms of the enzyme. The chemical modifications of L-gulonolactone oxidase which will be carried out include use of an antibody L-gulonolactone oxidase complex, conjugation with polyethylene glycol, with homologous albumin or with other circulating proteins. These procedures will be tested for their ability to synthesize ascorbic acid in vivo and maintain guinea pigs in an ascorbic acid independent state. Immune response, toxicity, distribution, fate, and other pharmacologic problems associated with enzyme administration will be studied. Techniques developed in this study should be helpful in developing approaches to enzyme replacement therapy for the more complex and less treatable enzyme dificiency diseases in man.